At least 10 injured in St Petersburg supermarket explosion

At least 10 people have been injured in an explosion at a supermarket in St. Petersburg on Wednesday, Russian officials said.

The Investigative Committee, the nation's top investigative agency, said a device containing 200 grams of explosives went off at a storage area for customers' bags. 

The Investigative Committee said the blast injured four people, while St. Petersburg officials said there were ten injured. 

One person is said to be in serious condition after the detonation of the improvised explosive device. 

"All possible versions of what has happened are being worked on," Alexander Klaus, the head of St Petersburg's investigative committee, said 

"As of now, it has been established that 10 people were taken to the city's hospitals with injuries. At the moment, the lives of those injured are not under threat."

Russian President Vladimir Putin has described the blast as a terrorist act

President Vladimir Putin described the blast at the Perekrestok supermarket chain late on Wednesday, as a terrorist act.

No one has claimed responsibility for the attach at the supermarket in the city’s northwest  Kalininsky district. 

The property was quickly evacuated and there were no reports of a fire, but images circulating on social media in Russia showed extensive damage in an area of the store close to the tills.

Officials had earlier suggested the attack was being treated as attempted murder.

Earlier this month, the Russian president and his US counterpart Donald Trump spoke by phone after information provided by the CIA helped Russian security services foil an attack on St Petersburg's Kazan cathedral.

At the time, Russia's Interfax news agency reported that a group had been planning attacks at a number of sites. Several people were reportedly detained.